Field of the Invention
The present invention relates generally to pipe metallurgy and manufacturing processes and, more specifically, to a stainless steel with a chemistry that is compatible with Electric Resistant Welding (ERW) for the manufacture of corrosion and/or erosion resistant stainless steel (PIPE) for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, and process pipe for mining, refining, power generating and petrochemical plant piping systems.
The compatible stainless steel(s) of this invention is a low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) stainless steel containing 10.5 to 14% chromium content by weight and/or a low carbon (0.080% maximum content by weight) martensitic stainless steel containing 10.5 to 14% chromium content by weight. The Laser weld process without filler metal and the ERW process conducted without filler metal as described herein eliminate filler wire melted weld metal and minimize the weld's Heat Affected Zone (HAZ) resulting in superior weld ductility compared to a like chemistry welded by Tungsten Inert Gas (TIG), Gas Metal Arc Weld (MIG), Plasma Arc (PLASMA), Submerged Arc Welding (SAW), or Double Submerged Arc Welding (DSAW) methods with filler metal. Also the ERW manufacturing method is more cost effective than production of seamless pipe of like chemistry, LASER welded pipe of like chemistry without filler metal and welded pipe of like chemistry with filler metal. This method also includes an optional post continuous induction or gas fired heat treatment of the martensitic weld HAZ.
Description of the Prior Art
Down-hole pipe, line pipe, and process pipe (PIPE) is used for production of oil and gas and liquids, gas and/or slurry transportation systems in the oil and gas, petro-chemical, refining, power generating and mining industries. PIPE may be installed in both vertical and horizontal planes with the plane being dependent on the application in which the PIPE is to be utilized. In addition, the PIPE may be subjected to corrosive environments containing small to substantial quantities of carbon dioxide and other corrosive elements or compounds. Also erosive conditions may exist in liquids, gas or slurry containing abrasive particles. In recent years, work has been done to develop PIPE that exhibits improved corrosion resistance to failure from CO2 stress corrosion cracking and corrosion pitting; and improved erosion resistance from abrasive materials in liquids, gas and slurries being transported by the PIPE.
PIPE subjected to these conditions may fail in a relatively short time due to such factors as stress corrosion cracking, intergranular corrosion and general corrosion metal loss. Wall loss may also be caused by erosion. The failure characteristic of steel PIPE may be influenced by many factors, including the chemistry of the steel, steel microstructure, the mechanical processing of the steel and the nature of the heat treatment which may be provided.
In regard to corrosion, one commonly used method of preventing corrosion in PIPE at the present time is to coat the inside diameter surfaces with a thin layer of an anti-corrosive material. The primary purpose of such coating is to extend the operational life of the PIPE by providing a physical barrier between the corrosive agent and the base metal. Typical coating materials include paints, phenolic compounds, epoxies, urethanes, and nylon compounds.
Another way to prevent corrosion and/or erosion is to make the PIPE out of a “Corrosion/Erosion Resistant Alloy”(CERA). Such CERA materials include, for example, the five alloys in the stainless family defined as martensitic, dual phase (martensite and ferrite), ferritic, austenitic, and duplex (austenite plus ferrite). Dual phase (ferrite plus martensite) is a stainless steel whose microstructure at room temperature consists of ferrite and martensite due to a special chemical balance. Martensitic stainless steel is one that has a martensite microstructure. Duplex (austenitic/ferrite) is a stainless steel whose microstructure at room temperature consists primarily of a near equal volume percent of austenite and ferrite. The term ferritic describes chromium stainless steels with a ferrite microstructure. Chromium stainless steels are divided into two classifications, hardenable and non-hardenable. When rapidly cooled from elevated temperatures the non-hardenable grades (ferritic) have a ferritic microstructure. The hardenable grades (martensitic) will exhibit a martensitic microstructure when rapidly cooled to room temperature. Austenitic denotes low carbon, iron-chromium-nickel stainless alloys containing more than 16% chromium, with sufficient nickel to stabilize austenitic microstructure at room temperature. These alloys cannot be hardened by heat treatment, but can be hardened by cold working. Such grades are normally non-magnetic, but can be slightly magnetic depending upon composition and amount of cold working. Classification or definition of the individual stainless steel family members is determined by the steel's chemical balance and resulting crystal structures as follows:    1) Austenite: a solid solution of one or more elements in face-centered cubic crystal structure.    2) Ferrite: a solid solution of one or more elements in body-centered cubic crystal structure.    3) Martensite: a solid solution of one or more elements in a tetragonal crystal structure. The martensitic microstructure is characterized by an acicular, or needle-like, pattern microstructure. Commercial examples of such classes of materials are martensitic seamless PIPE with 13% chromium content by weight used for down-hole oil and gas applications, austenitic pipe with 22% chromium and 42% nickel content by weight used for down-hole production of oil and gas, duplex stainless steel with 22% chromium and 5% nickel content by weight used for down-hole production of oil and gas and austenitic stainless steel 316L pipe used for line pipe to transport liquid and gas and for in-plant process pipe that are sold by the John Gandy Corporation of Conroe, Tex. The key alloy additions for Type 316L corrosion resistance is chromium with molybdenum added for superior resistance to pitting corrosion. Type 316L stainless steel exhibit different degrees of corrosion resistance both with or without a passive film depending on the corrosion environment. A passive film will not exist under the condition of erosion.
The above noted problems and other similar corrosion and/or erosion conditions make it desirable to provide a stainless steel PIPE. However, the introduction of stainless steel poses additional challenges for the manufacture of PIPE of the type under consideration. There are two well known commercial processes in use for manufacturing prior art steel PIPE such as those used in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, and process pipe for mining, refining, power generating and petrochemical plant piping systems. These processes produce either “seamless” steel pipe or they produce “welded” steel pipe. In general, a seamless steel pipe is produced by preparing a solid billet, forming a hollow shell by a method such as Mannesmann piercing, press piercing or hot extrusion, and rolling the thus-formed hollow shell by a rolling mill such as an elongator, plug mill or a mandrel mill and subjecting the rolled hollow shell to a sizing work performed with a sizer or a stretch reducer, whereby the final pipe product of a predetermined size is obtained.
In a typical prior art process, a seamless PIPE is manufactured, for example, from a billet of steel about 10 inches in diameter and 6 to 8 feet long. After heating to over 1000 degrees C., a hole is pierced through the center to form a very thick-walled tube. Hot rolling and cold drawing then progressively reduces the wall thickness and diameter of this tube until it is sized for the particular end purpose. Seamless is a costly method of manufacture; restricted both in size of outside diameter and in length.
Welded PIPE, on the other hand, is made from a flat strip referred to as plate or coil, which is formed into a PIPE and the two longitudinal edges of the plate or coil are welded to each other along the PIPE's length. There are seven typical and traditional welding methods utilized in the manufacture of welded PIPE. These methods are Laser, Tungsten Inert Gas (TIG), Gas Metal Arc Weld (MIG), Plasma Arc, Submerged Arc Welding (SAW), Double Submerged Arc Welding (DSAW) and Electric Resistance Welding (ERW). Additional care is necessary to avoid structural and cosmetic defects in the weld and the weld zone. Since such problems cannot arise from a seamless pipe, the seamless manufacturing process offers advantages in many situations. However, the cost incurred with the manufacture of seamless PIPE, and particularly the manufacturing restriction of certain larger sizes and longer lengths, together with the difficulties attendant upon the known processes of producing such PIPE, and the lack of uniformity with respect to successive PIPES has, to a large extent, driven the industry to the use of welded PIPE. Welded PIPE is the least costly method of manufacture and is not restricted in outside diameter and normally not restricted in length; and is equal in quality to seamless.
Another characteristic of welded PIPE versus seamless PIPE is that welded PIPE manufactured by TIG, MIG, Plasma Arc, SAW, or DSAW traditionally use filler metal. Laser and ERW welding processes do not use filler metal. Successful welding of typical dual phase (ferrite plus martensite), martensitic, ferritic, austenitic, and duplex (austenite and ferrite) stainless steels with 10.5 to 24% chromium content by weight, historically and traditionally has been restricted to TIG, MIG, Plasma Arc, SAW, and DSAW welding methods. To the applicant's knowledge the ERW method has not been practiced on dual phase (ferrite plus martensite), martensitic, ferritic, austenitic, and duplex (austenite and ferrite) stainless steels with 10.5 to 14% chromium content by weight for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, and process pipe for mining, refining, power generating and petrochemical plant piping systems. By the “ERW method” is meant a process for manufacturing a pipe from strip, sheet or bands by electric resistance heating and pressure, the strip being a part of the electric circuit. The electric current, which may be introduced into the strip through electrodes or by induction, generates the welding heat through the electrical resistance of the strip. Also to the applicant's knowledge the ERW method has not been practiced on low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic 10.5 to 14% chromium content by weight stainless steel PIPE for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems.
The present invention has as one object to manufacture corrosion and/or erosion resistant stainless steel PIPE by the ERW welding method without a filler metal from low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic 10.5 to 14% chromium content by weight stainless steel PIPE for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems.
Another object of the present invention is to manufacture corrosion and/or erosion resistant ERW welded PIPE without filler metal from low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) with 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic stainless steel with 10.5 to 14% chromium content by weight for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems that is more commercially economical than stainless steel PIPE with 10.5 to 14% chromium content by weight traditionally welded by TIG, MIG, Plasma Arc, SAW and DSAW with filler metal for like piping systems which are more costly due to slow forming and welding speeds and the cost of filler metal when compared to the ERW process.
Another object of the present invention is to manufacture corrosion and/or erosion resistant ERW welded PIPE without filler metal from low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) with 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic stainless steel with 10.5 to 14% chromium content by weight for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems that is equal in base metal mechanical properties but exhibits superior weld ductilities due to low heat input, resulting in a very narrow weld bond line and heat affected zone (HAZ) when compared with other stainless steel PIPE with 10.5 to 14% chromium traditionally welded by TIG, MIG, Plasma Arc, SAW and DSAW with filler metal for like piping systems.
Another object of the present invention is to manufacture corrosion and/or erosion resistant ERW welded PIPE without filler metal from low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) with 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic stainless steel with 10.5 to 14% chromium content by weight for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems that is equal or superior in quality when compared to 10.5 to 14% percent chromium content stainless steel pipe traditionally welded by TIG, MIG, Plasma Arc, SAW or DSAW methods with filler metal that often incur the problem of producing low ductility welds with excessively large weld metal deposits and wide HAZ due to the high heat induced by the method. This problem is compounded by weld metal (melted filler wire) dilution by the base metal.
Another object of the present invention is to manufacture ERW corrosion and/or erosion resistant welded PIPE without a filler metal from low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) with 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic stainless steel with 10.5 to 14% chromium by content by weight for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems that is more commercially economical than seamless stainless steel PIPE with 10.5 to 14% chromium content manufactured by the pierced billet method.
Another object of the present invention is to manufacture ERW corrosion and/or erosion resistant welded PIPE without a filler metal from low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) with 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic stainless steel with 10.5 to 14% chromium content by weight for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems that is equal in mechanical properties to seamless stainless steel PIPE with 10.5 to 14% chromium content by weight manufactured by the pierced billet method.
Another object of the present invention is to manufacture ERW corrosion and/or erosion resistant welded PIPE without a filler metal from low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) with 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic stainless steel with 10.5 to 14% chromium content by weight for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems that is equal in quality to seamless stainless steel PIPE with 10.5 to 14% chromium content manufactured by the pierced billet method.
Another object of the present invention is to manufacture PIPE without a filler metal for use in down-hole applications for oil and gas production, line pipe for transportation of liquids, gas and slurry, process plant, power generating and/or refining piping systems from low carbon (0.080% maximum content by weight) dual phase (ferrite plus martensite) with 10.5 to 14% chromium content by weight stainless steel and/or low carbon (0.080% maximum content by weight) martensitic stainless steel with 10.5 to 14% chromium content by weight by the ERW welding method that results in a very narrow bond line and HAZ in addition to a low carbon soft martensite in the HAZ producing a much more ductile weld than the weld of stainless steel with 10.5 to 14% chromium content by weight PIPE welded by TIG, MIG, Plasma Arc, SAW and DSAW methods.